Jack the car up in the rear and turn one wheel, if the other turns in the same direction, then it is a LSD, if turns in the opposite diretion, then it is not. Like yeros said, the gearing could be different, and that's what the other two numbers will indicate. Usually the Euro CSi's had 3.25 (39/12). I think there may be another number on the LSD that would indicate if its a 25% or 40% or.. That, I don't know where to find.

the differential is out of the car...sitting on the ground...so turn one output flange and the other side should turn the same direction if it is LS?